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ACCEPT_FILTER(9)	 BSD Kernel Developer's	Manual	      ACCEPT_FILTER(9)

NAME
     accept_filter, accept_filt_add, accept_filt_del,
     accept_filt_generic_mod_event, accept_filt_get -- filter incoming connec-
     tions

SYNOPSIS
     #include <sys/types.h>
     #include <sys/module.h>
     #include <sys/socket.h>
     #define ACCEPT_FILTER_MOD
     #include <sys/socketvar.h>

     int
     accept_filt_add(struct accept_filter *filt);

     int
     accept_filt_del(char *name);

     int
     accept_filt_generic_mod_event(module_t mod, int event, void *data);

     struct accept_filter *
     accept_filt_get(char *name);

DESCRIPTION
     Accept filters allow an application to request that the kernel pre-
     process incoming connections.  An accept filter is	requested via the
     setsockopt(2) system call,	passing	in an optname of SO_ACCEPTFILTER.

IMPLEMENTATION NOTES
     A module that wants to be an accept filter	must provide a struct
     accept_filter to the system:

     struct accept_filter {
	     char    accf_name[16];
	     void    (*accf_callback)(struct socket *so, void *arg, int	waitflag);
	     void *  (*accf_create)(struct socket *so, char *arg);
	     void    (*accf_destroy)(struct socket *so);
	     SLIST_ENTRY(accept_filter)	accf_next;   /*	next on	the list */
     };

     The module	should register	it with	the function accept_filt_add(),	pass-
     ing a pointer to a	struct accept_filter, allocated	with malloc().

     The fields	of struct accept_filter	are as follows:

     accf_name	       Name of the filter; this	is how it will be accessed
		       from userland.

     accf_callback()   The callback that the kernel will do once the connec-
		       tion is established.  It	is the same as a socket	upcall
		       and will	be called when the connection is established
		       and whenever new	data arrives on	the socket, unless the
		       callback	modifies the socket's flags.

     accf_create()     Called whenever a setsockopt(2) installs	the filter
		       onto a listening	socket.

     accf_destroy()    Called whenever the user	removes	the accept filter on
		       the socket.

     The accept_filt_del() function passed the same string used	in
     accept_filter.accf_name during registration with accept_filt_add(), the
     kernel will then disallow and further userland use	of the filter.

     The accept_filt_get() function is used internally to locate which accept
     filter to use via the setsockopt()	system call.

     The accept_filt_generic_mod_event() function provides a simple way	to
     avoid duplication of code for accept filters which	don't use the argument
     field to load and unload themselves.  This	function can be	used in	the
     moduledata_t struct for the DECLARE_MODULE(9) macro.

SEE ALSO
     setsockopt(2), accf_data(9), accf_http(9),	malloc(9)

HISTORY
     The accept	filter mechanism was introduced	in FreeBSD 4.0.

AUTHORS
     This manual page was written by Alfred Perlstein, Sheldon Hearn and
     Jeroen Ruigrok van	der Werven.

     The accept	filter concept was pioneered by	David Filo at Yahoo!  and re-
     fined to be a loadable module system by Alfred Perlstein.

BSD				 June 25, 2000				   BSD

NAME | SYNOPSIS | DESCRIPTION | IMPLEMENTATION NOTES | SEE ALSO | HISTORY | AUTHORS

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